Figure 4.

Schematic of the possible conduction channels in Mg-doped GaInN. (in all the mechanisms the surface layer is n-type degenerate) (a) Bulk layer is p-type. (b) The p-type conductivity occurs in the bulk layer below a certain depth from the
surface [20,29]. (c) The p-type conductivity is not within a uniform layer but occurs through p-type
percolation channels [30,31].